1. Field of the Invention
The present invention relates to a method for enabling scalable progressive downloading of video signals.
2. Description of the Prior Art
As AV content is digitized, the digitized content may be recorded in a recording medium such as a disk and transferred to users. In addition, with the development of networks, the digitized content may be stored in a server. Therefore, users can receive the content through networks and reproduce the received content through their terminals, e.g., PCs, thereby viewing the content.
A method for receiving and reproducing the content data through networks as described above includes a streaming scheme and a download scheme. In the streaming scheme, content data are received and simultaneously decoded, so that the decoded data are presented to users. In the download scheme, all of the content data are received and stored as a file and data of the stored file are sequentially read for decoding.
The streaming scheme is advantageous in that it can present the content data directly without long waiting time (but buffering time for some data is required). However, the streaming scheme is disadvantageous in that the content data cannot be moved or copied to other media because the content data are not stored as a file, and users must receive the content data again through networks when the users want to view the content data again. Differently from the streaming scheme, the download scheme is advantageous in that the content data can be moved or copied to other media because the content data are stored as a file. However, the download scheme is disadvantageous in that more time is required because presentation of the content data is performed after all the content data have been received.
A progressive downloading scheme is a scheme for overcoming disadvantages of the two schemes as described above. According to the progressive downloading scheme, data in the previously recorded file are read, decoded and outputted while currently downloaded content data are stored as a file. Further, some of the data are stored as a file and directly decoded without waiting time, and the file data can be repeatedly viewed after the initial viewing because the received data are stored as the file. In addition, the data may be copied or moved to other media.
However, because content data stored in and provided from a server must be provided with Quality of Service (QoS) according to network load or capability of a terminal, it is preferred to encode the content data by a scalable video or audio codec scheme. For example, according to a Scalable Video Codec (SVC) scheme, video signals are encoded with the best quality, but videos with low quality can be expressed even when a partial sequence (a sequence of a frame intermittently selected from the whole sequence) of a picture sequence created through the encoding is decoded for use.
Accordingly, a content server stores a content data file obtained by encoding video signals with the best quality, and transmits a picture sequence suitable for current conditions, i.e., a current bandwidth of a network, rendering capability of a terminal, etc., from the file, thereby causing the picture sequence to be decoded. That is, the data (scalable data) encoded by the scalable scheme may also be transmitted while some data in the file are skipped during transmission according to the current transmission states.
According to the progressive downloading scheme as described above, received data are stored as a file, i.e., meta data (representing subsidiary information of the file, a timing index, etc) of a content file initially transmitted from a server are stored at a corresponding position of the file, and then the content data are stored. However, if the content data are partially received due to the scalable characteristics, the content data do not correspond to the information of the meta data recorded in the specific position of the file. That is, a loss block having no content data occurs at a position designated by the meta data. Therefore, when the stored file is read and reproduced again depending on the meta data, there is an attempt to decode the data loss block, which may cause unexpected errors.